JP2631493B2 - Manufacturing method of corrosion resistant permanent magnet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an Fe-BR-based permanent magnet having high magnetic properties and having an oxidation-resistant coating excellent in salt spray resistance, and in particular, The present invention relates to a method for producing a corrosion-resistant permanent magnet having a coating with excellent salt water resistance and having extremely stable magnet properties without coating peeling in practical use under a use condition such as an automobile magnet which is affected by salt damage and the like.

BACKGROUND ART First, B and Fe are used as main components using lightly rare earths that are resource-rich, mainly Nd and Pr, and expensive Sm and Co are not essential.
Fe-BR-based permanent magnets have been proposed as new high-performance permanent magnets that greatly exceed the highest characteristics of conventional rare-earth cobalt magnets (JP-A-59-46008, JP-A-59-894).
No. 01).

However, Fe-
Permanent magnets made of BR-based magnetically anisotropic sintered bodies contain a large amount of rare earth elements and iron, which are easily oxidized in the air and gradually produce stable oxides. In such a case, the oxides generated on the surface of the magnet cause a decrease in the output of the magnetic circuit and variations between the magnetic circuits, and there is a problem of contamination of peripheral devices due to the loss of the surface oxide.

Problems of the prior art To improve the corrosion resistance of the above Fe-BR permanent magnet,
A permanent magnet in which the surface of a magnet body is coated with a corrosion-resistant metal plating layer by an electroless plating method or an electrolytic plating method (JP-A-60-1985)
No. 54406) and a permanent magnet having excellent oxidation resistance obtained by laminating an oxidation-resistant coating and a resin layer on the surface of a magnet body (JP-A-60-6390).
No. 2) has been proposed, but in this plating method, an acidic solution or an alkaline solution is used as a pretreatment method for plating, and since the permanent magnet body is a sintered body and is porous, plating is performed in this hole. An acidic solution or an alkaline solution remained in the pretreatment, and there was a possibility of corrosion with aging.

In addition, since there are metallic foreign substances such as black scales and oxide layers on the surface of the sintered magnet body, there is a problem that plating nonuniformity, adhesion and corrosion resistance are inferior. Inferior, there is a problem that the magnet surface is corroded during plating.

In addition, when left in an atmosphere at a temperature of 125 ° C and a relative humidity of 85% for a long time (PC / T test), the oxidation-resistant coating peels off, and the magnet properties after the test deteriorate from the initial magnet properties. The characteristics were unstable.

Further, an oxidation-resistant permanent magnet formed by laminating a conversion coating and a resin layer on the surface of the magnet body was tested in a salt spray test for 10 minutes.
There was a problem of rusting in less than 0 hours.

Object of the Invention The present invention aims to improve the adhesion of the salt water resistant coating provided on the Fe-BR permanent magnet and to solve the above-mentioned practical problems, and in particular, conforms to JIS Z 2371. Constant temperature and humidity cycle test (CC ・ C) including salt spray test (SMT)
-In the case of performing T), the salt water resistant coating is not peeled off, the deterioration from the initial characteristics is small, and Zn or Zn
The present invention aims at a production method capable of preventing the generation of white rust from alloy plating and preventing the white rust from falling off and providing an Fe-BR-based permanent magnet having stable high magnet properties at low cost. Excellent adhesion of the oxidation-resistant coating provided on the Fe-BR-based permanent magnet, especially in a constant-temperature and constant-humidity cycle test including a salt spray test, and at ambient conditions of a temperature of 125 ° C and a relative humidity of 85% Even if left for a long time, its adhesion does not deteriorate, and for the purpose of a stable Fe-BR-based permanent magnet without peeling of the oxidation resistant film, as a result of various studies on the surface treatment of the permanent magnet, Fe with specific components
After cleaning the surface of the -BR type sintered permanent magnet by shot blasting, after coating Zn or Zn alloy by electrolytic plating, performing chromate treatment, and further laminating an oxidation resistant resin, Has excellent adhesion,
The inventors have found that stable and excellent magnet properties with excellent corrosion resistance can be obtained, and have completed the present invention.

That is, the present invention relates to R (R is at least one of Nd, Pr, Dy, Ho, and Tb, or La, Ce, Sm, Gd, Er, Eu, Tm, Yb, Lu,
The surface of the sintered permanent magnet body mainly composed of 10% to 30% by atom, B2% to 28% by atom, and 65% to 80% by atom of Fe, and the main phase is a tetragonal phase Is cleaned by shot blasting, that is, a hard powder composed of at least one powder having an average particle size of 20 μm to 350 μm and a Mohs hardness of 5 or more is applied to the surface of the magnet body at a pressure of 1.0 kg / cm ^{2 to} 6.0 kg / of pressurized gas with cm ^2, 0.5
Min to 60 minutes, after removing the oxidized layer and the work strain layer on the surface of the magnet body, and then forming a single layer or a laminated metal layer of Zn or Zn alloy by an electrolytic plating method, on the metal layer A method for producing a corrosion-resistant permanent magnet, characterized by forming a oxidation-resistant resin layer by dipping or electrodeposition coating in a resin solution in which the non-volatile residue is reduced to a required concentration, or by resin coating. .

Effects of the Invention According to the manufacturing method of the present invention, when the magnet is left for a long time in a state of spraying a salt solution having a temperature of 35 ° C. and a concentration of 5%,
It is possible to obtain a highly practical Fe-BR-based permanent magnet in which the generation and detachment of white rust of the salt water-resistant coating composed of the resin and the metal coating layer are prevented, and the film adhesion is not deteriorated.

By the way, in the case of the conventional method in which a metal layer of Zn or a Zn alloy is applied to the surface of the Fe-BR based sintered magnet body and subjected to chromate treatment, black scale remaining on the surface of the sintered magnet body,
Or, depending on the processed layer, in the film peeling test using an adhesive tape before the corrosion resistance test, the problem that the film easily peels off, and the white rust generated in the constant temperature and humidity test (60 ° C x 90%) drops off, and the adhesion of the film Had a problem of deterioration.

However, in the present invention, on the surface of the sintered magnet body,
Before electroplating a metal layer of Zn or Zn alloy, the surface of the sintered magnet body is subjected to a shot blast treatment,
By performing a chromate treatment after the formation of the metal layer and further impregnating or applying a resin layer thereon, the initial adhesion of the plating film as compared with the case of simply plating the cleaned magnet body surface The rust generation time can be greatly delayed, and the generated white rust can be fixed with resin to completely protect the permanent magnet against changes in the external environment such as humidity and gas. be able to.

Constitution of the invention Under the shot blast condition of the present invention, as the hard powder having a Mohs hardness of 5 or more, powders of Al ₂ O ₃ system, silicon carbide system, ZrO ₂ system, boron carbide system, garnet system, etc. can be used. high Al ₂ O ₃ system powder are preferred hardness, as the powder form that amorphous are preferred.

If the Mohs hardness of the hard powder for shot blasting is less than 5, the grinding power is too small, and the grinding process takes a long time, which is not preferable.

When the average particle size of the hard powder is set to 20 μm to 350 μm, if the average particle size is less than 20 μm, the grinding force is too small and a long time is required for grinding, and if it exceeds 350 μm, the surface roughness of the surface of the sintered magnet body is increased. Is too coarse, and the grinding amount is not uniform, which is not preferable.

When the pressure of the hard powder is less than 1.0 kg / cm ² , the grinding process requires a long time, and the pressure is 6.0 kg / cm ^2.
If it exceeds, the amount of grinding of the magnet body surface becomes non-uniform, and there is a concern that the surface roughness may deteriorate.

Further, if the injection time is less than 0.5 minute, the amount of grinding becomes small and non-uniform, and if it exceeds 60 minutes, the amount of grinding on the surface of the magnet body becomes large and the surface roughness is unfavorably deteriorated.

As the pressurized fluid for injection of the hard powder, air or an inert gas such as Ar or N ₂ gas can be used.In order to prevent oxidation of the magnet body, an inert gas is preferable.
When air is used, dehumidified air is desirable.

The thickness of the surface layer to be removed by the shot blasting is preferably 10 μm to 20 μm, and the surface roughness of the obtained magnet body is preferably 1 μm to 3 μm.

In the present invention, a single layer of Zn or a Zn alloy plating is coated on the surface of the shot-blasted magnet body by electrolytic plating, or a Zn plating layer is laminated and coated on the Zn alloy plating.

As the Zn alloy layer, in the case of a Zn-Ni alloy, the Ni content is preferably 5 to 20 wt%, in the case of a Zn-Co alloy, the Co content is preferably 0.5 to 1 wt%, and in the case of a Zn-Cr alloy, The Cr content is preferably 1 wt% or less, and in the case of a Zn—Fe alloy, the Fe content is 5 wt% to 30 watts.
t% is preferred.

The pH of the plating solution for performing electroplating is pH 3 to 10
The bath composition is preferably a sulfuric acid acidic bath or an ammonium chloride bath.

Further, a polymer such as gelatin or demostrin is added to improve the throwing power of the plating layer, and other pH adjusting reagents and the like are mixed.

In the present invention, shot blasting physically removes black scales or processed layers remaining on the surface of the sintered magnet body, so that there is no deterioration due to pretreatment with an acidic or alkaline solution as in the conventional method.

The thickness of the plating is preferably 15 μm or less, more preferably 3-5 μm of Zn-Ni plating.
After having a thickness of m, Zn plating of 1 μm or less is applied.

After the Zn plating, 10 to 30 vol.
After immersion treatment for 2 seconds, it is washed with water and immediately subjected to chromate treatment.

This chromate solution has a chromium content of 1 to 20 g / l and further contains sulfuric acid, nitric acid, acetic acid, phosphoric acid, and the like.

The thickness of the chromate coating layer is preferably 0.1 μm or less.

In the present invention, the resin to be applied to the chromate coating layer is a coating resin such as an epoxy resin, a fluororesin, a thermosetting acrylic resin, a phenol resin, a melamine resin, and a silicone resin. The solid resin content is 5 wt%. ~ 2
By making it 0 wt% and diluting with a solvent, the effect of permeability to the chromate film can be increased.

If the solid resin content of the resin liquid is less than 5 wt%, the resin layer formed on the chromate coating surface of the sintered magnet body is thin and the corrosion resistance effect is small, and if it exceeds 20 wt%, the viscosity of the resin solution increases. This is not preferable because the permeability to the chromate film decreases and the corrosion resistance deteriorates.

The application to the chromate coating layer is performed by vacuum impregnation of the resin solution, by a dipping method, a spraying method, etc., after applying to the chromate coating layer of the sintered magnet body, followed by baking.
By applying this resin layer at a thickness of 1 μm or more, the moisture resistance is improved, but in order to obtain excellent dimensional accuracy, the thickness is preferably 5 μm or less.

Reasons for Limiting Components of Permanent Magnet The rare earth element R used in the permanent magnet of the present invention has a composition
Occupies at least 10 at% to 30 at%, but at least one of Nd, Pr, Dy, Ho, and Tb, or further, La, Ce, Sm, G
Those containing at least one of d, Er, Eu, Tm, Yb, Lu, and Y are preferable.

Usually, one kind of R is sufficient, but in practice, a mixture of two or more kinds (mish metal, dymium, etc.) can be used for reasons such as convenience in obtaining.

Note that R may not be a pure rare earth element, and may contain impurities which are unavoidable in production within the industrially available range.

R is an essential element in the above permanent magnet,
If the content is less than 10 atomic%, the crystal structure becomes a cubic structure having the same structure as that of α-iron, so that high magnetic properties, particularly high coercive force cannot be obtained. As a result, the residual magnetic flux density (Br) decreases, and a permanent magnet having excellent characteristics cannot be obtained. Therefore, the rare earth element is 10 atomic%
Within the range of 30 atomic%.

B is an essential element in the permanent magnet according to the present invention, and if less than 2 atomic%, the rhombohedral structure becomes the main phase,
High coercive force (iHc) cannot be obtained.
Since a B-rich nonmagnetic phase increases and the residual magnetic flux density (Br) decreases, an excellent permanent magnet cannot be obtained. Therefore, B is in the range of 2 to 28 atomic%.

Fe is an essential element in the above permanent magnets, and 65
If it is less than 80 atomic%, the residual magnetic flux density (Br) decreases,
If Fe exceeds 3, a high coercive force cannot be obtained, so Fe is contained in an amount of 65 to 80 atomic%.

Further, in the permanent magnet of the present invention, substituting part of Fe with Co can improve the temperature characteristics without impairing the magnetic characteristics of the obtained magnet, but the amount of Co substitution is reduced by Fe.
If it exceeds 20%, the magnetic characteristics deteriorate, which is not preferable. The substitution amount of Co is 5 atomic% to 15 in the total amount of Fe and Co.
In the case of atomic%, since (Br) increases as compared with the case without substitution, it is preferable to obtain a high magnetic flux density.

Further, the permanent magnet of the present invention can tolerate the presence of unavoidable impurities in industrial production in addition to R, B, and Fe.

For example, part of B is replaced with at least one of C of 4.0 atomic% or less, P of 3.5 atomic% or less, S of 2.5 atomic% or less, and Cu of 3.5 atomic% or less, with a total amount of 4.0 atomic% or less. As a result, the productivity of the permanent magnet can be improved and the price can be reduced.

Further, at least one of the following additional elements is Fe-B
-It can be added to the R-based permanent magnet because it has an effect of improving the coercive force and the squareness of the demagnetization curve, improving the productivity, and reducing the price.

9.5 at% or less Al, 4.5 at% or less Ti, 9.5 at% or less V, 8.5 at% or less Cr, 8.0 at% or less Mn, 5.0 at% or less Bi, 9.5 at% or less Nb, 9.5 at% or less Atomic% or less Ta, 9.5 atomic% or less Mo, 9.5 atomic% or less W, 2.5 atomic% or less Sb, 7 atomic% or less Ge, 3.5 atomic% or less Sn, 5.5 atomic% or less Zr, 9.0 atomic % Or less of Ni, 9.0 at% or less of Si, 1.1 at% or less of Zn, and 5.5 at% or less of Hf. However, when two or more kinds are contained, the maximum content is By containing at most atomic% of the additive element having the maximum value,
It is possible to increase the coercive force of the permanent magnet.

It is indispensable that the main phase of the crystal phase be tetragonal in order to produce a sintered permanent magnet having better magnetic properties than a fine and uniform alloy powder.

The permanent magnet of the present invention has an average crystal grain size of 1 to 80 μm.
A compound having a tetragonal crystal structure in the range of m as a main phase and containing a nonmagnetic phase (excluding an oxide phase) of 1% to 50% by volume.

The permanent magnet according to the present invention exhibits a coercive force iHc ≧ 1 kOe, a residual magnetic flux density Br> 4 kG, and a maximum energy product (BH) max
Indicates (BH) max ≧ 10MGOe, and the maximum value reaches 25MGOe or more.

The main component of R of the permanent magnet according to the present invention is
In the case where 50% or more is occupied by light rare earth metals mainly composed of Nd and Pr, R12 atomic% to 20 atomic%, B4 atomic% to 24 atomic%, Fe7
When 4 atomic% to 80 atomic% is the main component, (BH) max35
It shows excellent magnetic properties higher than MGOe, especially when the light rare earth metal is Nd, its maximum value reaches 45MGOe or more.

Further, in the present invention, in a corrosion resistance test in which an environment of 80 ° C. and a relative humidity of 90% is left for 500 hours or more for a long time, as permanent magnets exhibiting extremely high corrosion resistance, Nd 11 at% to 15 at%,
Dy0.2at% ~ 3.0at%, and the total amount of Nd and Dy is 12at% ~ 17at
%, B5at% ~ 8at%, Co0.5at% ~ 13at%, Al0.5a
It is preferable that the composition contains t% to 4 at%, C is 1000 ppm or less, and the balance is Fe and unavoidable impurities.

EXAMPLES Hereinafter, the present invention will be described with reference to Examples and Comparative Examples.

As starting materials, 99.9% pure electrolytic iron, ferroboron alloy containing 19.4% B, Nd and Dy with a purity of 99.7% or more are used.
An ingot having a composition (at%) of -0.5Dy-7B-78.5Fe was obtained.

Thereafter, the ingot was finely pulverized to obtain a finely pulverized powder having an average particle size of 3 μm.

This finely pulverized powder is charged into a mold of a press device, oriented in a magnetic field of 12 kOe, and formed at a pressure of 1.5 ton / cm ^{2 in} a direction parallel to the magnetic field. After sintering under the condition of Ar atmosphere for 2 hours, further aging treatment of 800 ° C x 1 hour and 575 ° C x 1 hour is performed in Ar atmosphere, diameter 12mm x
A test piece having a thickness of 2 mm was prepared.

Next, Al ₂ O ₃ powder having an average particle size of 100 μm was
It injected 20 minutes with dehumidified clean air pressure 2.0 kg / cm ^2,
The oxide layer and the work strain layer on the surface were removed to a thickness of about 17 μm, the surface roughness was adjusted to about 1 to 3 μm, and then Zn-Ni alloy plating was performed.

This Zn-Ni alloy plating is performed by adding 70 g / l of zinc chloride, 95 g / l of nickel chloride, 235 g / l of ammonium chloride, sodium naphthalene sulfonate, gelatin and the like as a brightener, and ammonia water as a pH adjuster. Using the first
Adjust to pH conditions as shown in the table.

The magnet test piece was electrolyzed in the Zn-Ni alloy plating bath at the temperature and plating conditions shown in Table 1 and immediately washed with water to perform Zn plating.

This Zn plating is zinc sulfate 410g / l, aluminum chloride
20g / l, sodium sulfate 75g / l, other dextrin, thiourea, sodium saccharin, boric acid, etc. are added to improve the throwing power. Using sulfuric acid as a pH adjuster, adjust to pH conditions as shown in Table 1. I do.

The magnet test piece plated with Zn-Ni alloy in this Zn plating bath was electrolyzed at the temperature and plating conditions as shown in Table 1, immediately washed with water, and immersed in dilute nitric acid (2 vol%) for 10 to 30 seconds. After the immersion treatment, a chromate treatment is performed.

This chromate solution is treated with a solution obtained by adding phosphoric acid or the like to 10 to 30 g / l of chromic anhydride for 30 to 60 seconds.

 Table 1 shows Zn-Ni alloy films and Zn films of the obtained magnets.

Further, the magnet test piece was washed with a solvent and dried, and then immersed in a non-volatile residue 10 wt% silicone resin solution.
The coating was applied to the surface of the magnet body and baked at 150 ° C. for 1 hour, and an oxidation resistant resin of 1 to 5 μm was provided on the chromate film.

The test piece was subjected to a moisture resistance test, and the results are shown in Table 1.

As a comparative example, a test piece having the same composition as in Example 1 was used.
A salt water test and a moisture resistance test were performed when a Zn—Ni alloy electrolytic plating layer was formed on the surface of the sintered magnet without performing shot blasting before forming the electrolytic plating film layer. Shown in the table.

In Table 1, the salt spray test (SMT) is based on JIS
FIG. 6 shows the deterioration of the test piece under the conditions of a 5% NaCl solution at 35 ° C. and at a temperature of 60 ° C. and a relative temperature of 90% in accordance with Z 2371. The adhesion test was performed by a cross-cut test after the moisture resistance test, and the adhesion strength test was based on JIS 6852.

Claims (1)

(57) [Claims] 1. R (R is at least one of Nd, Pr, Dy, Ho, Tb or La, Ce, Sm, Gd, Er, Eu, T
m, Yb, Lu, and Y) at least 10 at% to 30 at%, B 2 at% to 28 at%, Fe 65 at% to 80 at%, and the main phase is from tetragonal phase After the surface of the sintered permanent magnet body is cleaned by shot blasting, Zn or a Zn alloy is coated in a single layer or a laminated layer by electrolytic plating, and then the metal layer is subjected to chromate treatment. A method for producing a corrosion-resistant permanent magnet, comprising forming a layer.